Unbearable rich exhaust smell in well sealed cabin

[shaggy911]

I got a 95 gt convert thats got cams, heads and a MSD computer with a good tune. It runs rich. The narrow band stoich meter keeps jumping from lean to rich at idle, runs rich at cold start.

The convert cabin has good seals, i dont feel a draft at all. But at a light or when i start it, i cant stand the smell of rich exhast.

What is causing this? I smell this without running the fan. If i run vent, the smell dissipates a bit. All gauges show normal. Is it cats, injectors, o2 sensors? It has got exhaust headers and an xpipe (i think).

Where could the fumes enter the cabin from, if the convert/weatherstipping seals well?

 

[Venom351R]

Sure you dont have an exhaust leak somewhere? The cabins in the cars are not air tight there is still air vents and area's along the firewall for smells to come from.

First of all if it has a good tune why is it running rich? Second did you mean an MSD box or coil? I was not aware MSD made computers.

 

[64post]

I have a `94 GT coupe with headers, X-pipe and cat back system, I have had similar issues at stop signs or in stop and go traffic. I have had a local muffler shop as well as myself check extensively for any ex.leaks and never found any. It's annoying as hell but learning to live with it.Open your window from time to time so you don't get sick or pass out.

 

[HISSIN50]

The Narrowband gauge oscillates back and forth, which indicates a normal burn, yet you say it runs rich. Do you have a wideband? Smell is not a good indicator of air-fuel trim.

Do you run cats? Probably not.

As noted, look for an exhaust leak. Using smoke can be helpful.

Other areas to check are around the shifter on a manual car and the e-brake area.

Pull codes as well.

Good luck.

 

[shaggy911]

Thanks for your replies folks..


When the weather improves I can check if there is an exhaust leak. Right now we have 6 hours of reasonable sunlight when it isnt raining (Seattle)
thanks for suggesting to use smoke. Is there a chemical with which i can create good amount of smoke safely?

Not sure why it is running rich if the car is so well tuned. Previous owner tuned it - which i am beginning to doubt. It runs well. The cam needs a lot of revs so it stalls at low rpms.

I meant MSD box and coil - not the computer. The computer is from an fox mustang. The car was tuned specifically for that computer some time ago.

No wideband. i dont know the costs. If i can get a used one i will install it.

Have to check if it has cats or not.

couldnt pull codes at oreillys. The guy said the unit couldnt link well after positive hookup. apparently some fuse may be out... will hunt that tomorrow.

 

[blksn955.o]

Check your EVAP (charcoal canister under passenger fender has vacuum lines going to it) canister and vacuum lines.

Check the smog pump hose under the car that runs from the smog pump at the front of the engine to the x-pipe. If the smog pump is deleted make sure the lines are all blocked off.

On the test make sure the tester is being hooked up to the under hood OBDI test port and not the OBDII test port in the cabin (interior). The OBDII test port was only functional for V6 models.

 

[COBRA90GT]

I'd check the factory holes along the firewall - possibly missing a rubber grommet or two or three and that's allowing the smell inside the cabin...

 

[94 Black GT]

Mine did that ended up being an exhaust leak!! Tightened everything up and it was all better!! Hope that helps

 

[dcs7941]

I'd also check the fuel filler neck grommet. Mine had moisture around the rubber seal and where the neck sticks in the tank. The smell of gas was so stong I thought I had a major exhaust leak. I purchased a gromment and replaced the old one. Problem is solved.

 

[LethalInjection]

What kind of cam and exhaust are you running? They both can play a role in this as well.

 

[94 Black GT]

my car had an exhaust leak and it would do this..and it was definately unbearable..

 

[cjones]

you can check the codes yourself. there should be a how-to in the fox5.0 section.

running rich at startup is normal. it's called OPEN loop (a preset fuel strategy that doesn't use the O2 sensors).

as Hissin said, it's normal for the O2's to bounce lean-rich.

 

[BlackVert]

my bet is on a leak near on in the engine bay area that is coming through the vents or firewall